1. Field of the Invention
This invention relates to a method for predicting the time of occurrence, scale and focal region of an earthquake wherein the long electromagnetic waves or earth currents generated as premonitory symptoms of an earthquake are measured and a tomograph of the source region is prepared from the results of the measurement.
2. Prior Art Statement
The conventional method of predicting earthquakes, which has been put into regular practice in some areas, involves the simultaneous measurement of pre-earthquake long waves or earth currents at a number of points. More specifically, in the conventional method the pre-earthquake long waves or earth currents are measured simultaneously at two or more points on the earth surface, and the point of origin of the electromagnetic waves or earth currents (hereinafter referred to as the "wave source") is computed from the amplitude ratio of the detected signals. (See, for example, P. Varotsos and K. Alexopoulos: Tectonophysics, 110, pp73-98 (1984) and P. Varotsos and K. Alexopoulos: Tectonophysics, 110, pp99-125 (1984).
The margin of prediction error by the conventional method is .+-. one week in terms of time, .+-.0.5 in terms of magnitude and .+-.50 km in terms of location of the focal region. Moreover the method does not enable prediction of the shape, size, or time-course changes of the source region of the pre-earthquake long waves and earth currents and it has been impossible with the method to depict a three dimensional representation of the wave source region. As a result, while the prediction error has been generally within the requirements of society as regards quake magnitude and focal region, the time error has been two orders of ten greater than what is acceptable.
There is also known a method of finding the wave source using a directional antenna (see, for example, T. Yoshino: Proceedings of 1985 International Symposium on Antennas and Propagation, 243-4, Kyoto, Japan). In this case too, however, it has not been possible to depict a three dimensional representation of the wave source region due to the difficulty in detecting the angle of elevation of the wave source direction and further to the large degree of error in the azimuth. For this reason, the error in determining the focal region, which is substantially coextensive with the wave source region, becomes large, as do the errors in the earthquake magnitude (which is a function of the size of the wave source region) and in the time of earthquake occurrence (which is a function of time-course changes in the wave source region).
The present inventor previously proposed a method of picking up long electromagnetic waves and earth currents generated as premonitory symptoms of earthquakes in such manner as to discriminate the same from long waves and earth currents caused by man-made noise, static and the like Japanese Patent Disclosure Sho 63-184088 and (U.S. Ser. No. 138,947).